Milling process for preparing flake gold



United States Patent MILLING PROCESS FOR PREPARING FLAKE GOLD 2 Claims, No Drawings US. Cl 241/16;

Int. Cl B02c 17/00, B02c 19/12,C22b 11/04 Field of Search 241/3, 16,

22/(Metal Digest), 30, 15; 252/514; 106/306, 309, 308(f), 290; 75/05, 83

[56] References Cited UNITED STATES PATENTS 1,954,462 4/1934 Tainton 241/3 2,002,891 5/1935 Hall 241/3 2,263,603 11/1941 Ziehl 241/16 2,274,766 3/1942 Ziehl 241/3 2,668,749 2/1954 McHan 241/16 3,126,293 3/1964 McSheehy... 241/15 3,301,494 1/1967 Tomqvist.... 241/16 Primary ExaminerRobert C. Riordon Assistant ExaminerDonald G. Kelly Att0rny-lohn J. Klocko III ABSTRACT: Milling a gold powder which is a gold/mercury alloy containing 1-10 percent by weight mercury in a liquid system which contains a solvent, l20 percent of a fatty acid,

and, optionally, up to 1 percent finely divided rhodium for a MILLING PROCESS FOR PREPARING FLAKE GOLD BACKGROUND OF THE INVENTION Gold powder can be made by many precipitation reactions. For example, chemical reduction from acid solutions may be accomplished by the use of ferrous sulfate or oxalic acid; chemical reduction from alkaline solutions can be accomplished with hydrazine sulfate. In addition, many metals in powder form (e.g., zinc, aluminum or magnesium) will displace gold from its halide solution to produce a gold powder. The gold powder produced by these conventional techniques have nodular or irregular particle shape; none of these prior gold powders are characteristic of a flake or waferlike gold.

These nodular gold powders have been used for many years in preparing decorative gold paints as well as printed circuit inks. However, it was hoped that flake gold would produce better results than nodular gold since experience with silver has shown that flake silver produces a smoother, more lustrous, more continuous film than nodular silver. Also, the

flake silvers are far easier to disperse in organic vehicles in the formation of paints and inks.

The successful process for manufacturing flake silver is to mill a precipitated silver powder for several days in a ball mill, utilizing a mill vehiclecomposed of soap and water. Application of this technique to the preparation of flake gold has been unsuccessful due to the formation of large lumps of gold. In addition, no polishing of the gold resulted. Therefore, there is a need for process of preparing flake-type gold so that metalizations containing same may be advantageously used in decorative gold paints and printed circuit inks.

SUMMARY OF THE INVENTION This invention relates to a process of preparing flake gold comprising milling a gold powder in a liquid system containing a liquid selected from the group consisting of hydrocarbons and chlorinated derivatives thereof, and l-20 percent by weight of a fatty acid for a sufficient time to produce gold flakes wherein there is no significant formation of gold lumps.

In addition, metalizing compositions comprising the gold flake are produced for decorative and electronic applications.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred process of preparing flake gold comprising milling a gold powder, which is a gold/mercury alloy containing I I percent by weight mercury, in a liquid system which consists essentially of (a) a liquid selected from the group consisting of aromatic hydrocarbons, acyclic hydrocarbons and chlorinated derivatives thereof, and (b) l percent of a saturated fatty acid, and 01 percent finely divided rhodium dispersed in said liquid system, for a sufficient time to produce gold flakes wherein there is no significant formation of gold lumps.

One of the most important aspects of this invention resides in the discovery that a fatty acid acts as a wetting agent, to coat the gold particles and prevent the particles from agglomerating. Various saturated and unsaturated fatty acids may be used; these include butyric acid, caproic acid, lauric acid, stearic acid, behenic acid, cerotic acid, oleic acid, linoleic acid, parinaric acid and erucic acid. The fatty acid shouldcomprise l-20 percent by weight of the liquid system to prevent the gold particles from agglomerating.

The milling may be carried out by any appropriate.

procedures which are well known to those skilled in the art. However, it has been found that glass beads produce gold flakes with very smooth surfaces. Glass beads provide a polishing action rather than a grinding action that would be produced by other common milling techniques, such as by porcelain milling.

The liquid system which is used as the milling medium must contain a liquid in which the fatty acid will dissolve. The function of the solvent is to dissolve the fatty acid so that the acid is molecularly distributed throughout the liquid system thereby permitting the acid to coat the gold particles. Many of the common organic solvents can be used for this purpose. In particular, aromatic hydrocarbons, acyclic hydrocarbons and their chlorinated derivatives may be used so long as the fatty acid is soluble in the liquid hydrocarbon or chlorinated derivative. Typical solvents include: xylene, toluene, benzene and trichlorethylene.

The term a gold powder is intended to include a metallic gold in physical or chemical combination with various other compatible metals. Mixtures of gold and other precious metals, alloys of gold and other metals, and various other combinations of other metals with gold are within the scope of this technology. A preferred gold powder is a gold/mercury'alloy containing ll0 percent by weight of mercury. It has been found that the alloying of mercury in the gold powder produces a gold flake that is harder, less malleable and does not contain lumps. Other metals such as platinum, palladium or silver may also be used in combination with the gold.

In another preferred aspect of this invention, small amounts.

of rhodium may be dispersed in the liquid system. Generally, 0-1 percent by weight of finely divided rhodium may be included in the liquid system to provide a harder and brighter polished gold flake.

The process should be carried out for a sufficient time to provide gold flakes which are hard, highly polished and do not contain any significant amount of lumps. In general, a sufficient milling time has been found to range from 8-100 hours. A preferred laboratory operating time is considered to be from 6070 hours.

The solids to liquid ratio may be adjusted to a desirable consistency. It is preferred to utilize a thin slurry of the gold powder in the liquid system so as to provide adequate separation between each of the gold particles. A solids (gold powder, rhodium, etc.) to liquid ratio ranging from l:l0 to 1:50 is operable.

The invention is illustrated by the following examples. in the examples and elsewhere in the specification, all parts, ratios and percentages of materials or components are by weight.

EXAMPLE 1 A gold/mercury alloy powder containing approximately 5 percent mercury was prepared as follows: A gold chloride solution was prepared by dissolving 1,200 gms. of metallic gold in aqua regia.

To the AuCl solution was added 1.5 gal. water and 84 gms. HgCl this mixture was stirred until the I'igCl crystals dissolved. Then 3 gal. of dilute NH OH was stirred into the AuCh/HgCl solution to produceauniform slurry. Fina|ly,an excess of dihydrazine sulfate, which had previously been dissolved in water, was added with constant agitation to the slurry. Finely divided nodular gold/mercury alloy powder was allowed to precipitate, separated from the slurry and then washed.

Into an 8-oz. glass jar with a screw lid, was placed 225 gms. A" glass beads, 50 gms. of the finely divided gold/mercury alloy powder prepared above, 60 cc. of xylene and 3 gms. stearic acid. The lid was secured on the jar and the closed jar was rotated on a ball millrack at l20 rpm. The milling operation was carried out for 65 hours. After this time the gold powder was filtered from the liquid system and washed. It was observed in the form of flake gold and displayed a bright appearance.

For purposes of further illustrating this invention the follow ing examples, as tabulated inTable l, are described. The same TABLE I 1 8 oz. glass jar. 1 qt. porcelain.

gold powder and procedures described in Example 1 were utilized. A gold flake having a bright appearance was produced in all examples.

A metalizing composition was prepared from the gold flake of Example 4. The composition contained 95 percent flake gold and percent of a finely divided inorganic binder (65 percent PbO, 25 percent SiO and percent B 0 dispersed in a vehicle consisting of 8 percent ethyl cellulose and 92 percent beta terpineol. This gold composition was printed in the form of electrodes on an alumina substrate and fired at 950C. Highly conductive, electrodes resulted.

The gold flake of this invention can be used'to prepare various metalizing compositions. In general, conductor compositions containing gold flake are more useful since a continuous gold film is desired in the ultimate fired structures. However, this does not limit the scope of the invention and the gold flake may also be used in various other metalizing compositions, such as resistor compositions. The metalizing compositions, which contain the gold flake may be dispersed in an inert vehicle. Additionally, metalizing compositions can also contain a -finely divided inorganic binder (e.g., glass, bismuth oxide,

cerium oxide, etc.); for example, 499 percent by weight of the flake gold and 1-96 percent by weight of an inorganic binder may be dispersed in an inert vehicle. Any of the conventional components and proportions of ingredients may be included in the metalizing compositions of this invention. For

propionates; the terpenes, such as pine oil, alphaand betaterpineol and the like; solutions of resin such as polymethacrylates of lower alcohols, or solutions of ethyl cellulose, and solvents such as pine oil and the monobutyl ether of ethylene glycol monoacetate. The vehicles of copending application, Ser. No. 617,855, may also be used. The vehicle may contain or be composed of volatile liquids to promote fast setting after application; or it may contain waxes, thermoplastic resins or the like materials which are thermofluids so that the vehiclecontaining composition may be applied at elevated temperatures to a relatively cold ceramic body upon which the composition sets immediately.

The proportions of inert vehicle: solids (flake gold, glass, etc.) in the metalizing compositions of this invention may vary considerably depending upon the manner in which the paint or paste is to be applied and the kind of vehicle usedv Generally, from 30-90 percent solids are dispersed in from 70-10 percent by weight of the inert liquid vehicle.

Since it is obvious that many changes and modifications can be made in the above-described details without departing.

from the nature and spirit of this invention, it is to be understood that the invention is not to be limited to said details except as set forth in the appended claims.

1 claim:

1. A process of preparing flake gold comprising milling a gold powder, which is a gold/mercury alloy containing l 10 percent by weight mercury, in a liquid system which consists essentially of (a) a liquid selected from the group consisting of aromatic hydrocarbons, acyclic hydrocarbons and chlorinated derivatives thereof, and (b) 1-20 percent of a saturated fatty acid, and 01 percent finely divided rhodium dispersed in said liquid system, for a sufficient time to produce gold flakes wherein there is no significant formation of gold lumps.

2. A process in accordance with claim 1 wherein the milling is carried out by the use of glass beads. 

